1. Field of the Invention
The present invention relates to an exchange coupled film, to a magnetoresistive element, and to a thin-film magnetic head.
2. Related Background Art
As the recording density of hard disk devices has risen, there has been an attendant need for higher performance in thin-film magnetic heads. One type of thin-film magnetic head that is widely used is a compound thin-film magnetic head having a structure in which a magnetoresistive (MR) element or other such magnetic detection element and an electromagnetic coil element or other such magnetic recording element are laminated. These elements are used to reproduce data signals from magnetic recording media, and to write data signals to magnetic recording media.
The magnetoresistive elements used in thin-film magnetic heads have a structure in which a non-magnetic layer is sandwiched between a pinned magnetic layer in which the direction of magnetization is fixed by an exchange coupled field applied from an antiferromagnetic layer, and a free magnetic layer in which the direction of magnetization is not fixed. The direction of magnetization of the free magnetic layer varies with the orientation of the magnetic flux emitted from the magnetic recording medium, and the resistance of the magnetoresistive element varies in proportion to the relative angle of the direction of magnetization of the pinned magnetic layer and the free magnetic layer. Accordingly, if the position of the magnetic recording medium relative to the thin-film magnetic head is moved while a constant current (sensing current) is allowed to flow to the magnetoresistive element, it is possible to read the data signal of the magnetic recording medium as a voltage signal, that is, to reproduce the data signal with the thin-film magnetic head.
As discussed above, the direction of magnetization of the pinned magnetic layer is fixed by an exchange coupled field applied from the antiferromagnetic layer, and the strength of the exchange coupled field, which determines the strength of fixing the direction of magnetization, is an important element for the reliability of a thin-film magnetic head. Specifically, if the exchange coupled field applied from the antiferromagnetic layer to the pinned magnetic layer is too weak, the direction of magnetization of the pinned magnetic layer may become angled to the original fixing direction during the operation of the thin-film magnetic head. If this should happen, the reproduction output of the thin-film magnetic head may decrease, or the asymmetry of the reproduced waveform may worsen.
To prevent such problems, the exchange coupled field applied from the antiferromagnetic layer to the pinned magnetic layer must be sufficiently strong. One technique for making this exchange coupled field stronger is to raise the crystallinity of the antiferromagnetic layer by using a suitable material for the buffer layer of the antiferromagnetic layer. For example, Japanese Laid-Open Patent Application H09-16915 discloses the use of a laminate of a tantalum layer and an NiFeCr layer or the like as a buffer layer for an antiferromagnetic layer, and Japanese Laid-Open Patent Application 2006-210907 discloses the use of a laminate of a tantalum layer and a ruthenium layer as a buffer layer for an IrMn layer, which is an antiferromagnetic layer.
Nevertheless, while the buffer layer of an antiferromagnetic layer in a conventional thin-film magnetic head does have the effect of strengthening the exchange coupled field applied from the antiferromagnetic layer to the pinned magnetic layer, there are cases when the exchange coupled field is still not strong enough, and the reliability of the thin-film magnetic head is diminished.
It is an object of the present invention to provide an exchange coupled film with higher exchange coupling strength than in the past, and a highly reliable magnetoresistive element and thin-film magnetic head in which this exchange coupled film is used.